1. Field of the Invention
This invention relates to a radiation image storage panel for recording and reproducing a radiation image using a stimulable phosphor which stores radiation energy and emits light upon stimulation thereof, and more particularly to a radiation image storage panel which provides a radiation image of high quality.
2. Description of the Prior Art
A novel method for obtaining a radiation image is disclosed, for example, in U.S. Pat. Nos. 3,859,527, 4,236,078 and 4,258,264. In the method of the patents, there is used a radiation image storage panel comprising a stimulable phosphor which emits light when stimulated by an electromagnetic wave selected from among visible light and infrared rays after exposure to a radiation. (The term "radiation" as used herein means electromagnetic wave or corpuscular radiation such as X-rays, .gamma.-rays, .beta.-rays, .gamma.-rays, high energy neutron rays, cathode rays, vacuum ultraviolet rays, ultraviolet rays, or the like.) The method comprises the steps of (i) causing the stimulable phosphor of the panel to absorb a radiation passing through an object, (ii) scanning the panel with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as "stimulating rays") to sequentially release the radiation energy stored in the panel as light emission, and (iii) detecting the emitted light and converting it into an image. The light emitted by the stimulable phosphor upon stimulation thereof is photoelectrically detected and converted to an electric signal by use of a photoelectric converter such as a photomultiplier. The electric signal can be processed in various ways as desired to reproduce a visible image of desired characteristics suitable for diagnostic purposes, which is a great advantage of this method using a radiation image storage panel.
The radiation image storage panel employed in the aforesaid method for recording and reproducing a radiation image has a phosphor layer comprising an appropriate binder and a stimulable phosphor dispersed therein. When the phosphor layer is self-supporting, the phosphor layer can by itself form the radiation image storage panel. In general, however, the phosphor layer is provided on an appropriate substrate to form the radiation image storage panel. Normally, a protective film for physically and chemically protecting the phosphor layer is provided on the phosphor layer on the side opposite to the substrate. In general, the protective film is constituted by a transparent thin film of polyethylene terephthalate, polyethylene, vinylidene chloride, nylon, or the like, and bonded to the surface of the phosphor layer by use of a transparent adhesive. Accordingly, an adhesive layer generally intervenes between the phosphor layer and the protective film. There are instances where a filter layer for absorbing the stimulating rays scattered in the protective film or the phosphor layer is formed betweeh the adhesive layer and the protective film. Further, a prime-coating layer is sometimes formed between the phosphor layer and the substrate for the purpose of increasing adhesion therebetween.
When the radiation image storage panel is used in the aforesaid method for recording and reproducing a radiation image, it is first exposed to a radiation passing through an object to have a radiation image of the object stored therein, and is then scanned with stimulating rays which cause it to emit light in the pattern of the stored image. The emitted light is photoelectrically converted into an electric signal in time sequence. In general, the exposure of the radiation image storage panel to stimulating rays is conducted from the protective film side of the panel. However, when the substrate of the radiation image storage panel is permeable to stimulating rays, the exposure of the panel to stimulating rays may be conducted from the substrate side of the panel.
Stimulating rays are selected among visible light and infrared rays. In order to separate stimulating rays from the light emitted by the radiation image storage panel upon stimulation thereof which, in many cases, is light having a wavelength within a region of ultraviolet rays to blue light, and to prevent the panel from being heated, the stimulating rays should preferably have a wavelength within the range of 450 nm to 1,100 nm, more preferably 500 nm to 750 nm. In general, because of high stimulation energy, coherent light having a single wavelength, particularly a laser beam such as an Ar-laser beam (488 nm), a He-Ne laser beam (633 nm), a ruby laser beam (694 nm), a YAG-laser beam (1,640 nm), or the like is employed as the stimulating rays.